This application relates generally to an animal holding device for holding an animal during an imaging operation.
More specifically, this application relates to an apparatus and method including a restraining assembly for an anaesthetized rodent (rats or mice or other) in combination with a split array coil for magnetic resonance imaging (MRI) the animal in real-time in a non-destructive manner.
Rodents and other laboratory animals are often used for testing purposes. Such testing may involve the need to scan the animal using a scanning device, such as an SPECT, PET, CT, CAT, X-Ray, NMR/MR, or other imaging device, to provide real time and/or photographic images of the animal, which may be done in a non-destructive manner. It is often desirable to anesthetize such animals in order to completely immobilize the animal during the scanning process. Anesthetized animals, and in particular rodents, often cannot hold their body temperature at desired temperatures during such procedures, potentially leading to stress on the animal.
A system and method of maintaining the body temperature of immobilized animals in a consistent state while the animal is being anesthetized and/or while the animal is being scanned, or otherwise utilized by the testing process was disclosed in U.S. patent application Ser. No. 12/430,487, filed on Apr. 27, 2009, and incorporated herein by reference. Jürgen E. Schneider et al.: “Ultra-Fast and Accurate Assessment of Cardiac Function in Rats Using Accelerated MRI at 9.4 Tesla. Magnetic Resonance in Medicine” 59: 636-641 (2008), also incorporated herein by reference, discusses such concepts.
With live animals, it is always desirable to keep the time of the experiment as short as possible so that the stress on the animal is kept to a minimum. An assembly where the skull is fixed at the position of the animal's ears with two pins that form a stereotactic holder provides a stereotactic fixation such that the position of the animal's skull is well defined. The usual neurological set-up of a life animal incorporates a minimum of 3 positioning points. This is the bar to fixate the animal's teeth, and two pins for the locking of the skull via the animal's ears (left and right). However, it is often difficult to find the correct pressure to securely fixate the animal and lock it securely in one position and not harm the animal (e.g. perforate its ear drums). Due to the set-up from both sides of the animal's head, it is relatively time consuming to lock the animal head and to position it in the centre of the assembly, and so poses additional stress to the animal. The stereotactic set-up with ear pins also consumes valuable space and so limits the coil's filling factor.
A head coil assembly used in MRI imaging can be either carried out as a cylindrical volume coil enveloping the animal, or as a surface coil or surface array positioned directly on top of the animal head. This MR volume coil has clear advantages when good homogeneity is desired, as the image intensity is distributed relatively even over the volume. A good homogeneity is very important for qualitative measurements and QA set-ups. However, a small positioning error can lead to large changes in the signal intensity, and affect the measurement. However the volume coil has a low sensitivity and the image SNR at the position of the animal brain is usually much lower than with a local surface coil positioned above the animal skull. Although the surface coil has clear SNR advantages over the volume coil, its signal sensitivity drops rapidly when moving away from the coil. So both, the penetration depth and the homogeneity of the surface coil are rather poor.
MR investigations of the animal's heart use a different set-up in comparison to neurological investigations of the animal brain. An assembly composed of one or more MR loops is housed inside a thin semi cylinder or a flat structure when imaging the heart. Here, the animal is usually positioned on top of the coil to reduce motion artefacts and also to minimize the distance of the coil to the animal's heart.
Desirable is a device for supporting the anesthetizing and scanning process that is compatible with desired scanning functions, such that the animal can be imaged in an optimum position and with a coil size that can be adjusted to the particular size of the animal's head for maximum filling factor and optimum signal-to-noise-ratio (SNR). Also desirable is positioning that can be reproduced in later experiments. It would also be useful to reduce or eliminate as much animal movement as possible to supress motion artifacts during an MR experiment, and to reduce setup times to minimize the stress of the animals.